There are conventional devices for recognizing character lines printed on media surfaces such as personal checks. For example, well-known are character recognition devices in which a character portion is detected from binary image data, the character portion is segmented along the bounding rectangular frame, character features are extracted from the obtained character pattern, the similarity between the feature vector of the input pattern and a standard vector for each character in the feature dictionary is obtained, and a character candidate is selected according to the degree of similarity.
Among such character recognition devices is one provided with various measures for re-binarization based on the recognition result in order to improve the recognition accuracy (see Patent References 1 through 3, for example).
More specifically described, in the technology disclosed in Patent Reference 1, it is judged according to the result of the character recognition and the counting result of the black points whether it is necessary to re-binarize the gray-scale image; if it is necessary, a threshold different from the original threshold is set and the gray-scale image is binarized using the new threshold. In the technology disclosed in Patent Reference 2, when a correct recognition result could not be obtained under the initial binarization condition, the filter or the threshold is changed based on the result of the total number of pixels having the same value and then the process from the preceding processing to the recognition processing is re-run. In the technology disclosed in Patent Reference 3, when the score which is the basis of the individual pattern comparison result is in a warning judgment frame which is set based on the sequential statistical processing result, the pickup system and the threshold are changed and then the process from the scanning to the recognition processing is rerun.    [Patent Reference 1] Japanese Patent Application H09-016715 Unexamined Publication    [Patent Reference 2] Japanese Patent Application H10-222602 Unexamined Publication    [Patent Reference 3] Japanese Patent Application 2004-118611 Unexamined Publication
However, in the technology disclosed in Patent Reference 1 only those results that do not satisfy the allowance range are re-binarized, but the judgment as to whether the threshold on the whole is appropriate or not is not performed; therefore, a question arises as to whether the recognition result is reliable enough. Also, the technology disclosed in Patent Reference 2 is also locally applied to only the characters that were not read, which is in the same manner as the Patent Reference 1; therefore, it is not sufficient to improve the reliability of the recognition result on the whole. Note that the technology disclosed in Patent Reference 3 re-scans the image, which is contrary to the demand for speedy processing.